JPH04280443A - Interconnection of electric parts on substrate - Google Patents

Abstract

PURPOSE: To provide a sealing method for a flip chip integrated circuit that completely covers a die surface and maximize an available area of a board. CONSTITUTION: An adhesive material 120 including a flux agent is coated on a board having a metallized pattern 110 or on an electric component 130 with a solder bump. The component 130 is placed on the board 110 and the solder bump 140 is subject to reflow. For the reflow stage, the flux agent promotes the the solder bump 140 to be soldered to the metallized pattern 110 and the adhesive material 120 is cured to interconnect the board 110 to the component 130 and to seal it.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD This invention relates generally to electronic circuits and more particularly to electrical interconnection methods.
and more particularly relates to flip chip mounting and encapsulation of integrated circuits.

0002

BACKGROUND OF THE INVENTION Solder bump interconnects were developed to eliminate the high cost, unreliability, and low productivity of manual wire bonding. Solder bump interconnect technology for flip-chip integrated circuits has been used in some form for approximately 20 years. Whereas early, less complex integrated circuits typically have peripheral connections, flip-chip bumping technology allows for a significant increase in interconnect density as it progresses to full-area arrays. did. Controlled collapse chip connections use solder bumps deposited on wettable metal terminals on the die and matching footprints of the wettable terminals with solder on the substrate. An upside-down integrated circuit (flip chip) is aligned to the substrate and all bonds are formed by reflowing the solder at the same time. In the controlled collapse method, bumps of solder are deposited onto the terminals of an integrated circuit, and the solder bumps are restrained from flowing out of the terminals by the use of a thick glass dam, and the tip of the substrate metallization is Solder flow is restricted. Similarly, solder flow on an integrated circuit is limited by the size of the solderable pads on the exposed metal on the surface of the chemically vapor deposited glass passivation on the integrated circuit.

[0003] The selection of solder alloy is determined based on its melting point. Lead-rich solders are used in joining integrated circuits to alumina ceramic substrates due to the high melting point of the alloy, allowing further processing of the assembled circuits. Bonding to organic carriers such as epoxy or polyimide circuit boards requires lower melting point solder alloys. Solders such as eutectic tin/lead solder (melting point 183°C) or lead/indium solder (melting point 220°C) have been used.

The choice of terminal metallurgy depends on the solder selected. Silver and gold are poor choices because they dissolve quickly into the solder. Therefore,
Copper, tin, lead, palladium, platinum, or nickel are commonly used for circuit board terminals, and thin films of chromium, titanium, or nickel are commonly used as integrated circuit terminals.

Solder bumps are placed on integrated circuit terminals while the die is still in wafer form. The final operation before cutting the wafer is an electrical test, where the soft solder serves to provide a contact pad for the mechanical probe used to contact the terminals.

To bond an integrated circuit to a substrate, a flux, water-white rosin or water-soluble flux, is applied onto the substrate as a temporary adhesive to hold the integrated circuit in place. The assembly is subjected to a reflow temperature cycle to bond the die to the substrate in an oven or furnace. The surface tension of the solder helps the die self-align with the terminals on the board. After reflow, flux residue must be removed to prevent corrosion of the die. Chlorine, fluorine or hydrocarbon solvents are used to remove rosin, or aqueous solutions of surfactants are used to remove water-soluble fluxes. Due to the close proximity of the die to the substrate (typically 0.0
01 to 0.004 inches, or 0.0254 mm to 0.102 mm), removing flux residue from under the die is a difficult task requiring sophisticated cleaning regimes and considerable time consumption. Ensuring complete removal of all flux residues has been the subject of many industrial efforts.

After cleaning, the assembly is electrically tested and packaging is added to provide additional environmental protection. Passivation, encapsulation, or adding a cover are common methods. For encapsulation, liquid polymer is added around and under the die. Historically, the polymer of choice has been silicones.
and epoxy, with epoxy being more preferred. Epoxy adheres better to ceramic substrates than silicone. The expansion coefficient of epoxies can be lowered by adding ceramic fillers. This reduces the thermal stress created between the substrate and the encapsulant. The importance of epoxy adhesives with low coefficients of expansion cannot be overemphasized for flip chip applications. Cured epoxy is stiff and does not have the flexibility of silicone. Therefore, if their coefficient of expansion is not lowered by the filler, early device failure can result from the formation of cracks in the die. The use of inorganic fillers also affects thermal conductivity and ionic contaminant levels.

The very small gap between the die and the substrate must be completely filled to provide maximum environmental protection for the device. Past efforts to encapsulate devices have left a void area in the center of the die, organic resin is added around the die, and the space is removed, as described in U.S. Pat. was drawn in by capillary action. As the size of the die increased, the limited effectiveness of capillary action became more subtle and larger areas of the die remained unprotected.

[0009]

Other methods of encapsulating the surface of a die have attempted to overcome the above limitations by applying organic resin through a hole in the substrate located in the center of the die. After soldering and cleaning operations, encapsulant resin was applied to the holes and also around the periphery of the die to ensure complete coverage of the die surface. This method creates the need to reserve areas of the board free of circuitry to provide unused space for the holes.

Clearly, there is a need for an improved method of encapsulating flip chip integrated circuits that ensures complete coverage of the die surface and allows maximum use of the available area of the substrate.

[0011]

[Means and effects for solving the problems] Briefly stated, according to the present invention, a fluxing agent (fluxing agent) is used.
An adhesive material containing a solder-bumped electrical component is applied to a substrate having a metallization pattern or a solder-bumped electrical component. The component is placed on the board and solder reflowed. During the reflow step, the fluxing agent promotes adhesion of the solder to the metallization pattern of the substrate and the adhesive material is cured to mechanically interconnect and encapsulate the substrate and components.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a substrate 100 having a metallization pattern 110 is selectively coated with an adhesive material 120 by screen printing, stenciling, preform application, or other dispensing means. Adhesive material 120
The material is formulated to include a fluxing agent and a curing agent so that the material does not cure immediately at room temperature. An example of a suitable adhesive material is an epoxy resin made from bisphenol A and epichlorohydrin. The curing or curing agent may be an amine, anhydride, or a suitable reactant. Other two-material resin systems such as polyester resins with appropriate curing agents can be used instead. The purpose of the fluxing agent is to provide a fluxing action for the soldering operation. abietic acid, adipic acid,
Ascorbic acid, acrylic acid, citric acid, 2-furoic acid, malic acid, and polyacrylic acid have been found to be useful as fluxing agents. Other organic acids of the general formula are also useful, where R is an electron withdrawing group (elec
tron with drawing grorp)
It is. Particular electron-withdrawing groups are fluorine, chlorine, bromine, iodine, sulfur, nitrile, hydroxyl, benzyl or some other electron-withdrawing group.

The amount of fluxing agent in the adhesive material ranges from about 0.1 to about 16% depending on the specific fluxing agent activity, the selected solder alloy, and the substrate metallization system.
% by weight.

Device 130 including solder bumps 140
Solder bumps 140 and active surface 150 are positioned facing substrate 100 and aligned with metallization pattern 110 of substrate 100 . Referring to FIG. 2, bumped device 230 is moved into intimate contact with metallization pattern 210. The adhesive 220 is attached to the device 230
to ensure complete coverage of the active surface 250 of the device 230. Meniscus 260 is active surface 2
A continuous encapsulation is provided around the periphery of the device 230 to protect the device 50 from environmental contamination. A fluxing agent contained in adhesive 220 covers solder bumps 240 and metallization pattern 210.

Although the drawing depicts device 130 as an integrated circuit encapsulated and connected to a substrate, it is understood that embodiments using other types of surface mount elements with solder bumps are within the scope of the invention. You should understand.

Assembly 270 is reflowed in a traditional manner to allow the fluxing agent to be activated, reduce oxides on the solder 240 and metallized surfaces 210, and allow alloying of the solder to the metal. . During the reflow process, the adhesive 220 is cured to a solid state. Depending on the chemistry of the adhesive system used, a second post-cure operation may be required to fully cure adhesive 220. During the reflow/cure step, the device is encapsulated with adhesive. meniscus 2
40 provides a continuous encapsulation around the periphery of the device 230 to protect the active surface 250 from environmental contamination, so no further cleaning or encapsulation operations are required.

The following examples are illustrative of the manner in which the invention may be practiced and are not intended to unduly limit its scope.

EXAMPLE 1 An adhesive material containing a fluxing agent and a hardening agent was prepared according to the following formula. component

Weight% Furane 89
303 Epoxy, Part A 41
malic acid

4.6 Furane 89303
Epoxy, Part B 54.4

Furane 89303 epoxy, Part A, manufactured by Furane Products Comp, Los Angeles, California, USA.
It is a bisphenol A-epichlorohydrin type epoxy resin available from Any. It is formulated for use in encapsulating semiconductor devices. Furane
89303 epoxy, part B is also Fura
ne Products Company. Other types of two-part epoxies can also be used to achieve the desired results within the scope of this invention. Equivalent materials are Hysol, Amicon, and Reichhold
It is available from companies such as Chemical.

The malic acid and epoxy Part A are placed in an aluminum pan. The mixture was heated to approximately 150° C. with stirring until the solution became clear. The solution was cooled to room temperature, Part B was added to the pan, and the mixture was stirred until uniform. A portion of the mixture was spatula coated onto a copper-coated polyimide film and soldered with low temperature solder (63% tin, 3
A sphere of 7% lead) was placed on the surface of the mixture. 1. Polyimide film to ensure solder ball reflow
It was heated to a temperature exceeding 85°C. After approximately 30 seconds, the polyimide film was removed from the heat source and allowed to cool to room temperature. The solder balls were examined under a 30x microscope to determine the degree of reflow and wetting of the balls to the copper and to each other.

Approximately half of the solder balls coalesced to form a large mass, while the remainder did not coalesce and remained as a distinct sphere. This indicated that the solder was not wet enough to ensure complete reflow. The copper surface of the polyimide film was glossy and shiny where the adhesive was in contact with the copper, indicating removal of copper oxide. The adhesive material was found to be stiff and bond strongly to the copper. Differential scanning calorimetry testing of the adhesive indicated that the adhesive had cured.

Example 2 Another adhesive material containing a fluxing agent and a hardening agent was prepared according to the following recipe. component

Weight% Fura
ne 89303 epoxy, part A
43.3 Malic acid

11.4 Fura
ne 89303 epoxy, part B
45.3 Example 2 was constructed and tested in the same manner as above. The results showed that approximately 70% of the solder balls coalesced into a single mass.

Example 3 Another adhesive material containing a fluxing agent and a hardening agent was prepared according to the following recipe. component

Weight% Fura
ne 89303 epoxy, part A
41 Malic acid

16 Furane
89303 Epoxy, Part B 4
3 Example 3 was constructed and tested in the same manner as described above. The results showed that all the solder balls coalesced into a single mass, indicating complete and total wetting of the solder.

Example 4 Another adhesive material containing a fluxing agent and a hardening agent was prepared according to the following recipe. component

Weight% Shel
l Epon 825 epoxy resin
50 Malic acid

7 Methylhexahydrophthalic anhydride
42 Imidazole

1

[0025] Malic acid (maric acid)
acid) and epoxy were placed in an aluminum pan. The mixture was heated to approximately 150° C. with stirring until the solution became clear. The solution was cooled to room temperature and diluted with methylhexahydrophthalic anhydride (m
ethylhexahydrophthalic a
nhydride) and imidazole were added to the pan and the mixture was stirred until uniform.

A portion of the mixture was tested in the same manner as above. The results showed that 75% of the solder balls coalesced into a single mass, indicating incomplete wetting of the solder. This indicated that the solder was not wet enough to ensure complete reflow. The copper surface of the polyimide film was glossy and shiny where the adhesive was in contact with the copper, indicating removal of copper oxide. Sh
ell Epon 825 epoxy resin is 175-
Epoxy equivalent of 180 and 550 at 25°C
It is a high purity bisphenol A-epichlorohydrin epoxy resin with a viscosity of 0-6500 centipoise. It is available from Shell Chemical Company, Houston, Texas, USA, and the imidazole is available from Anhydri, Newark, New Jersey, USA.
de and Chemicals, Inc. Available from.

Example 5 Another adhesive material containing a fluxing agent and a hardening agent was prepared according to the following recipe. component

weight%
Furane 89303 epoxy, part A
43.5 Malic acid

12.5
Furane 89303 epoxy, part B
44 Example 5 was constructed and tested in the same manner as above. The results showed that all the solder balls coalesced into a single mass, indicating complete and total wetting of the solder. It was determined that the use of a lower amount of fluxing agent as compared to Example 3 was preferred and would be an example.

The formulation of Example 5 was used to coat five test substrates that were metallized to accept solder bumped output terminals of flip chip integrated circuits. The bumped integrated circuits were reflowed and electrically tested as described in the Examples. all 5
One circuit passed the electrical test. The soldered assembly was then subjected to thermal cycling by immersing it in alternating hot and cold liquid baths. The temperature of the heated bath was 125°C and the temperature of the cold bath was -55°C, and the soldered assemblies remained in each bath for 1 minute and were then immediately transferred to the other bath. Assembly is 1, 5, 10, 25, 50, 100, 1
They were submitted to the same electrical test regime after 25, 175, and 200 thermal cycles. All five assemblies passed the electrical test after 175 thermal cycles, with one assembly failing the test after 200 cycles.

The formulation of Example 5 was also used to coat three test substrates that were metallized to accept solder bumped output terminals of flip chip integrated circuits. The bumped integrated circuits were reflowed and mechanically tested as described in the Examples. The anvil of a force measuring tool was placed against the side of the integrated circuit and the force required to remove the integrated circuit from the substrate was recorded. The forces ranged from 3.8 to 4.7 newtons, with an average force of 3.9 newtons.

[0030]

As described above, according to the present invention, an adhesive having flux properties can be used to solder reflow and encapsulate surface-mounted components, particularly flip-chip integrated circuits, Provides complete environmental protection for active surfaces.

[Brief explanation of the drawing]

1 is a cross-sectional front view of a device prior to attachment to a substrate according to the invention; FIG.

FIG. 2 is a cross-sectional front view showing a device after reflow to a substrate according to the present invention.

[Explanation of symbols]

100,200 board 110,210 metallization pattern 120,220 Adhesive material 130,230 device 140,240 Solder bump 150,250 active surface 260 meniscus 270 Assembly

Claims (10)

[Claims] 1. A method of making electrical and mechanical interconnections between an electrical component and a component-mounted substrate, comprising: providing a substrate with a metallization pattern; applying an adhesive material including a fluxing agent to the substrate or the component; positioning the component on the substrate; and reflowing the solder bump, wherein the fluxing agent is attached to the substrate of the solder. an electrical connection between an electrical component and a component mounting substrate, characterized in that the adhesive material promotes adhesion to a metallization pattern and, when the adhesive material is cured, mechanically interconnects the substrate and the component. methods of making physical and mechanical interconnections. 2. The step of reflowing the solder is a step of heating the adhesive material at a first temperature to perform solder reflow, the fluxing agent promoting reflow of the solder bump, and the step of reflowing the solder bump. Add the adhesive material to the second
2. The method of claim 1, further comprising the step of curing the adhesive material by heating at a temperature of . 3. An adhesive material having a fluxing agent for use in solder reflow for interconnecting electrical components and substrates, comprising a thermosetting resin, a fluxing agent, and a hardening agent. Adhesive material with a fluxing agent. 4. The adhesive material of claim 3, wherein the fluxing agent comprises a compound having the following formula: where R is an electron-withdrawing group. 5. The fluxing agent of claim 3, wherein R is selected from the group consisting of fluorine, chlorine, bromine, iodine, sulfur, hydroxyl, nitrile, and benzyl. 6. The adhesive material according to claim 3, wherein the fluxing agent is malic acid. 7. The adhesive material of claim 3, wherein the proportion of fluxing agent in the adhesive material ranges from about 0.1 to about 16% by weight of the adhesive material. 8. An electrical component having a plurality of electrical terminations, each termination including a solder bump, a component mounting having a plurality of electrical terminations corresponding to the terminations of the electrical component. a substrate, an adhesive material for mechanically connecting the electrical component to the substrate, the adhesive material comprising an epoxy resin, a hardening agent, and a fluxing agent; and a substrate, the solder bumps being reflowed and electrically connecting the electrical component to the substrate. 9. The fluxing agent comprises a compound having the following formula: where R is fluorine, chlorine, bromine,
9. The electrical component assembly of claim 8, wherein the electron withdrawing group is selected from the group consisting of iodine, sulfur, hydroxyl, nitrile, and benzyl. 10. The electrical component assembly of claim 9, wherein the compound is malic acid.